The present invention relates to a novel absorbent article such as a sanitary napkin having an absorbent structure which is characterized by having multiple integral high absorbency zones disposed within its thickness.
Absorbent structures are known for inclusion in disposable absorbent articles used for absorbing body fluids and other exudates. Such absorbent structures have traditionally been made from readily available and relatively inexpensive materials such as cotton fibers, wood pulp fluff, cellulosic tissue or wadding, or other absorbent fibers. These materials have provided satisfactory absorbency of fluids both in terms of absorbency rate and overall absorbent capacity. Unfortunately, absorbent structures made from such materials may tend to collapse when wetted, thereby losing some of their void volume. Such structures may also allow absorbed fluid to be squeezed back out of the structure onto the user of the absorbent article. Furthermore, when such structures have absorbed fluid, they may present an uncomfortable wet feeling against the skin of the user.
More recently, superabsorbent polymer particles have been combined with the more traditional absorbent materials to provide structures with enhanced absorbency and retention, which may help to eliminate the above problems. Replacement of traditional absorbent materials with superabsorbent polymer particles may also allow for absorbent products to be thinner while retaining the absorbent capacity of thicker, bulkier products. A drawback to superabsorbent polymer particles, however, is their relatively high cost compared to the more traditional absorbent materials.
Additionally, since superabsorbent polymer particles tend to swell as they absorb fluid, they may cause what is commonly known as gel-blocking. In other words, as fluid is absorbed by the particles of superabsorbent polymer, those particles swell and may form an occlusive layer of swollen superabsorbent particles. This occlusive layer then prevents the passage of additional fluid into the structure. Thus, the superabsorbent polymer particles must be properly placed within an absorbent structure to allow for this swelling and to most fully utilize their absorbent capacity. Generally, prevention of gel-blocking has been realized by mixing superabsorbent polymer particles with spacer materials, such as absorbent or nonabsorbent fibers, or by placing the superabsorbent polymer particles toward the bottom of the absorbent structure. However, although these methods of superabsorbent polymer placement may minimize gel-blocking, they do not effect the most efficient use of the superabsorbent polymer""s absorbent capacity.
Therefore, what is needed is an absorbent structure with good absorbency and retention of fluid. What is also needed is an absorbent structure that helps to provide a dry feel to the skin of a user when used in an absorbent article. What is further needed is an absorbent structure with superabsorbent polymer particles spaced and placed within the structure to most fully utilize the absorbency and retention capabilities of the superabsorbent polymer particles.
It is an object of the present invention to provide an absorbent article with good absorbency and retention of fluid that will help to provide a dry feel to the skin of a user of the article.
It is another object of the present invention to provide an absorbent structure with superabsorbent polymer particles spaced and placed within the structure to most fully utilize the absorbency and retention capabilities of the superabsorbent polymer particles.
In accordance with the present invention, there has been provided a novel absorbent structure for use in absorbent articles. The absorbent structure includes an absorbent element having an integral structure formed from absorbent fibers and super absorbent particles. The absorbent structure may optionally include additional laminate layers such as one or more layers of tissue and/or a nonwoven fabric. The nonwoven fabric may have a lower density and a higher porosity than the absorbent element of the invention to allow for rapid fluid acquisition and the subsequent transfer of the acquired fluid to an adjacent, slower absorbing, higher density absorbent element. Alternatively, the nonwoven fabric may have a higher density and a lower porosity than the absorbent element to increase fluid wicking throughout the nonwoven fabric. Preferably, lower-density nonwoven fabrics are placed adjacent the body-facing surface of an absorbent element, and higher-density nonwoven fabrics are placed adjacent the garment-facing surface of an absorbent element.
The absorbent structure of the invention has peripheral edges and a center region. The center region is that portion of the structure which is inward from the peripheral edges of the structure and which is intended to accept incoming fluid when the structure is used in an absorbent article. The absorbent element also has peripheral edges and a center region (as described above). The peripheral edges of the absorbent element may be coterminous with the peripheral edges of the absorbent structure or may be inward from or extend beyond the peripheral edges of the absorbent structure.
The absorbent element has an upper surface and a lower surface defining therebetween an absorbent element thickness. The absorbent element further has an integral structure and further includes a first high absorbency zone and a second high absorbency zone separated from one another by a portion of the element thickness. Each of the first and second high absorbency zones comprises an integral mixture of absorbent fibers and superabsorbent polymer particles and has a first surface and a second surface. As used herein, the terminology xe2x80x9cintegralxe2x80x9d means a unitary structure wherein the absorbent fibers are intermeshed throughout the entire absorbent element. Thus, there are no identifiable laminate layers which are separable from other layers within the element. Consequently, the surfaces of the high absorbency zones are not, per se, identifiable surfaces. As used herein, the terminology xe2x80x9csurfacexe2x80x9d as it relates to each of the high absorbency zones represents the location at which a transition occurs from a section of the integral structure substantially free of superabsorbent polymer particles to a section of the integral structure containing a mixture of absorbent fibers and superabsorbent polymer particles.
The first surface of the first high absorbency zone may optionally be coplanar with the upper surface of the absorbent element, or alternatively, the first high absorbency zone may be below or spaced from the upper surface of the absorbent element wherein the upper surface is substantially free of superabsorbent polymer particles and contains only absorbent fibers. Subjacent to the first high absorbency zone is a second high absorbency zone, each zone having a respective thickness. The thickness of the first high absorbency zone may be the same as or different from the thickness of the second high absorbency zone. Preferably, the thickness of each of the first and second high absorbency zones comprises less than about 35% of the thickness of the absorbent element. More preferably, the thickness of each of the first and second high absorbency zones comprises less than 20% of the thickness of the absorbent element. The first high absorbency zone is separated from the second high absorbency zone by a portion of the absorbent element thickness which is substantially free of superabsorbent particles. Additionally, the portions of the absorbent element that are outside of the first and second high absorbency zones are substantially free of superabsorbent polymer particles.
The superabsorbent polymer particles are mixed with absorbent fibers within the first and second high absorbency zones. In a preferred embodiment, the superabsorbent polymer particles are uniformly and homogeneously mixed with the absorbent fibers within the first and second high absorbency. Alternatively, the superabsorbent particles may be distributed within one or both of the first and second high absorbency zones on an increasing gradient wherein the concentration of superabsorbent particles increases from a minimum at the first surface of the high absorbency zone to a maximum at the second surface of the high absorbency zone, or a decreasing gradient, wherein the concentration of superabsorbent particles decreases from a maximum at the first surface of the high absorbency zone to a minimum at the second surface of the high absorbency zone. Alternatively, the superabsorbent particles can be distributed in a manner such that a maximum concentration of these particles occurs in a region centered at approximately half the distance between the first surface and the second surface of one or both of the high absorbency zones.
In a most preferred embodiment the upper surface of the absorbent element is substantially free of superabsorbent particles, the first high absorbency zone being slightly below the upper surface of the absorbent element wherein the upper surface of the absorbent element comprises 100% absorbent pulp fibers.
In accordance with the present invention, there has been provided an absorbent structure utilized in absorbent articles such as sanitary napkins, diapers, incontinence articles and the like. An embodiment of such an article comprises the absorbent element of the invention contained between a liquid-permeable body-facing layer and a liquid-impermeable barrier layer and positioned such that the body-facing layer is adjacent the upper surface of the absorbent element and the impermeable barrier layer is adjacent the lower surface of the absorbent element.
Also provided in accordance with the present invention is a novel apparatus for intermittently applying a particulate material to a substrate, the apparatus comprising two applicator valve assemblies, each applicator valve assembly comprising a stationary funnel having an opening and positioned within a moveable housing such that the moveable housing is free to move relative to the stationary funnel, the moveable housing comprising at least one slot opening and at least one recycle hole spaced from the slot opening, wherein the moveable housing moves relative to the stationary funnel to provide an application phase to allow passage of particulate material by free-fall through the stationary funnel opening and the slot opening when the stationary funnel opening aligns with the slot opening, and a recycle phase to prevent dispensing of particulate material onto the substrate when the stationary funnel opening aligns with the at least one recycle hole.
Also provided in accordance with the present invention is a novel method for intermittently applying particulate material to a substrate comprising the steps of:
providing a substrate;
providing a continuous supply of first particulate material from a first supply source to a first valve having a powder application phase and a recycle phase;
disposing the first valve to the powder application phase to allow passage of first particulate material by free-fall therethrough;
dispensing the first particulate material through the first valve onto at least a portion of a surface of the substrate;
disposing the first valve to the recycle phase to prevent dispensing of first particulate material onto the substrate and to retain the first particulate material within the first valve;
conveying the first particulate material back to the first supply source;
providing a continuous supply of particulate material from a second supply source to a second valve having a powder application phase and a recycle phase;
disposing the second valve to the powder application phase to allow passage of second particulate material by free-fall therethrough;
dispensing the second particulate material through the second valve onto at least a portion of a surface of the substrate;
disposing the second valve to the recycle phase to prevent dispensing of second particulate material onto the substrate and to retain the second particulate material within the second valve; and
conveying the second particulate material back to the second supply source.